So much good input here.
I agree it sounds as though Kirkpatrick's 4th level of training assessment--results--may reveal the training indeed did not completely "stick".
Educators have learned that there's a limit to retention; reinforcement of instruction, hands on application and linking the learning to related tasks helps students remember. However, it doesn't always work. I've approached some reasons why in this article.
http://elsmar.com/Forums/showthread.php?t=12122
So, a thoughtful examination of various factors should be conducted. The more important details are, the more practical are visuals and ready procedures, including flow charts and sign off sheets. Are these performance aids being used? Is it clear that this leak test is very important and why?
How often is the leak test scheduled? A week is long enough to lose retention of some lessons or details within them.
Suppose it is a training matter. Does the student operator have a processing disorder (who knows? Sometimes the subject person doesn't know).
Is the trainer delivering manageable chunks of material in comfortable environments, with respect to learning styles and giving frequent hands-on reinforcement?
Is the student operator perhaps preoccupied with a personal matter like financial problems or a family medical crisis? Might his attention have wandered at some moment during the run through (demonstrating the task and "proving" training was effective) and he is afraid to say so now?
So many questions, so little time... Please do the 5-Whys with a Cause and Effect analysis and explore this matter thoroughly enough to ensure:
1. The operator is the right person for the job.
2. The trainer is sufficiently expert, spirited and organized enough to deliver and assess adequately.
3. Errorproofing aids are being used where practical so people don't have to remember trivia or peruse manuals that look like dictionaries just to do their jobs.
4. Employees come to work ready for work, and the environment helps them do their work well.
5. Employees are able and not afraid to tell you when something is amiss.